The present invention relates to wireless communication technology, and, more particularly, to methods, systems, and computer program products for allocating bandwidth in a radio packet data system.
A radio packet data system generally comprises an access network (AN), a plurality of access terminals (AT), and the air interface defined between the two. The AN may further comprise a plurality of base stations or sectors with each of the base stations/sectors having a radio footprint associated therewith that covers a certain geographical area, which may overlap with those of neighboring base stations/sectors. One design metric that may be used in a best-effort radio packet data system is the manner in which system resources are allocated to ATs based on the signal conditions that the ATs experience.
In general, a conventional best-effort radio packet data system may be designed to allocate system resources, such as frequencies and/or time slots, to ATs in a proportional and fair manner based on the quality of the radio channel conditions that the ATs are experiencing. The ATs may communicate information to the AN that describes the quality of the radio channel conditions. The feed back information may include signal strength information, an ATs preferred serving base station/sector and/or data rate.
For example, as described in the “cdma2000 High Rate Packet Data Air Inteface Specification,” Version 3.0, by the 3rd Generation Partnership Project 2, dated Dec. 5, 2001, the disclosure of which is hereby incorporated herein by reference, an AT may request data service from the AN by sending a message on the reverse link that indicates which base station/sector the AT prefers to receive data from and at what rate the data should be sent. The information fed back from an AT to the AN may be referred to as data rate control (DRC) information. In an HDR system, an AT determines the DRC information based on measurements taken during receipt of pilot symbols. FIG. 1A shows the time slot format of the HDR forward link channel. Each time slot is 1.66 ms long and has 2048 chips. The time slot is divided into two sub-slots. Each sub-slot or half time slot is further divided into a pilot chips field, which may be used for channel estimation and/or determination of DRC information, two medium access control (MAC) chips fields for control and signaling, and two data chips fields for data payload. The pilot field may be an all-one sequence and the MAC fields may contain control signaling, such as reverse power control commands and reverse activity indication. As shown in FIG. 1B, if a base station/sector does not have any data to send to the ATs in its coverage area, then the base station/sector transmits idle information during the data intervals.
In an HDR system, there are twelve data packet formats with nine different data rates ranging from 38.4 kbps to 2457.6 kbps. During a data service session, an AT monitors the pilot symbols on the forward link and maintains a list of potential serving base stations/sectors. On the reverse link, the AT sends a DRC message every slot that indicates from which base station/sector and at which one of the twelve data rates it intends to receive data.
The AN receives the requests from multiple ATs in the system and schedules the data delivery to the terminals through the requested base stations/sectors and at the requested data rates using time division multiplexing techniques in a manner intended to balance overall throughput and to provide fairness. Once the AN decides to serve or allocate bandwidth to an AT, it delivers the packets from the base station/sector requested by the AT and at the rate requested by the AT starting two slots after the transmission of the corresponding DRC information. For packets comprising multiple slots, the time slots are not transmitted consecutively. Instead, the time slots are separated by a 3-slot interval to allow time for acknowledgements from the AT to reach the AN.
As discussed above, the ATs determine the DRC information based on measurements taken during receipt of pilot symbols. Because the base stations/sectors are synchronized in time, the signal received by an AT during the pilot symbol interval is the superposition of the pilot symbols from potential serving base stations/sectors. Based on these measurements, an AT may determine the signal-to-interference ratio (SIR) over the pilot symbol interval for potential serving base stations/sectors and the one with the highest SIR is selected as the serving base station/sector. The highest sustainable data rate at this SIR may then be selected as the requested rate to be included as part of the DRC information to be fed back to the AN. Unfortunately, this may result in a more pessimistic data rate estimate than may otherwise be achieved inasmuch as all base stations/sectors transmit during the pilot interval and this may not always be the case during the data intervals.